Particleboard is the term used for products manufactured from lignocellulosic materials, usually wood, primarily in the form of discrete pieces or particles, combined with a synthetic resin and bonded together under heat and pressure. It may be made by either a wet process or a dry process.
It is widely used in the furniture trade where it can be used for cores over which are bonded fine veneers, decorative plastics, or other materials. It is also used in mobile homes, floor underlayments, decking, sheathing, wainscoting, baseboards, and the like.
Although there are hundreds of species of wood in a variety of sizes and shapes that have been used in the production of particleboard, only three types of resin have been used; namely, urea-formaldehyde, phenol-formaldehyde, and isocyanates.
Because of environmental problems and OSHA restrictions, it is necessary to find replacements for the formaldehyde-containing adhesive systems. The presence of even less than one percent of free formaldehyde, based on the total weight of the product, is undesirable, not only because of its unpleasant odor, but also because it is an allergen and an irritant, causing severe reactions in the operators who manufacture the adhesive system and who prepare and handle the particleboard and in persons who handle articles fabricated from the particleboard. In addition, because of their very dark colors, phenol-formaldehyde resins are not always suitable for decorative applications. The isocyanate systems have the disadvantages of high cost and the need for special handling because of their toxicity.
A typical resin for use in the manufacture of particleboard has a pH between about 6.8 and 7.8, a Brookfield viscosity between about 1.80 and 3.50 poises, and a solids content of about 65 percent in water. In addition, it has a storage stability of two weeks at 40.degree. C. with less than a doubling in viscosity.